THE METABOTROPIC GLUTAMATE-RECEPTOR MGLUR4, BUT NOT MGLUR1-ALPHA, IS PALMITOYLATED WHEN EXPRESSED IN BHK CELLS

Several G protein-coupled receptors have been shown to be palmitoylated, and for some of these receptors the covalent attachment of palmitate has been implicated in the regulation of receptor-G protein coupling. The metabotropic glutamate receptor (mGluR) family forms a distinct group of G protein-coupled receptors, and the possibility that these may also be palmitoylated has been examined. Clonal baby hamster kidney (BHK) cells permanently transfected with the mGluR4 and mGluR1 alpha subtypes were labelled with [H-3]palmitic acid. The cells were lysed, the receptors were immunoprecipitated with specific antipeptide antibodies, and the immunoprecipitates were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and autoradiography. The palmitoylated, endogenously expressed G protein alpha-subunit alpha(q) could be immunoprecipitated from [H-3] palmitate-labelled BHK cells expressing mGluR1 alpha using a specific antipeptide antibody, but in the same cell lysates no detectable [H-3] palmitate-labelled mGluR1 alpha was found. This suggests that this mGluR subtype, associated with stimulation of phospholipase C, is not palmitoylated. In contrast, mGluR4, which is coupled to inhibition of adenylyl cyclase, was found to be labelled with [H-3]palmitic acid, and the palmitate was quantitatively removed by treatment with 1 M hydroxylamine, suggesting attachment of the palmitate through a thioester bond. Stimulation with maximal doses of the neurotransmitter glutamate for 1, 5, or 10 min appeared to have no effect on the level of receptor palmitoylation.